Optical ribbon cables and stranding method

Abstract

A method of stranding light waveguide ribbon cables, such as slotted core type cables, including stacks of light waveguide ribbons. A radially inward light waveguide ribbon in a stack is stranded at a lower tension than a radially outward light waveguide ribbon in the stack. The stack of light waveguide ribbons may be disposed in other slotted carriers such as U-shaped members or folded tapes.

What is claimed is: 
     
       1. A method for making a light waveguide ribbon cable, comprising: forming a central element having a longitudinal axis;   disposing a carrier about said central element, said carrier including a helical slot which is open radially outward with respect to said central element axis;   providing at least first and second relatively flat optical waveguide ribbons, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces; and,   applying a first tension to said first ribbon and applying a second tension to said second ribbon while inserting said ribbons in said slot to form a radially superimposed stack, said first ribbon in said stack being located at a radially inward position and said second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said central element, and said second tension exceeding said first tension.   
     
     
       2. A method as set out in claim 1, wherein said ribbons are unwound from spaced-apart payoff sheaves, and said ribbons are separated from each other for at least a predetermined distance prior to being inserted into said slot. 
     
     
       3. A method as set out in claim 1, wherein the difference in the tensions applied to said ribbons is at least 10 g. 
     
     
       4. A method as set out in claim 1, wherein during ribbon stranding the strain in the central element is greater than the strain in either of said ribbons. 
     
     
       5. A method as set out in claim 1, wherein the central element comprises an axial strength member. 
     
     
       6. A method as set out in claim 1, further comprising applying a moisture-absorptive tape about said carrier. 
     
     
       7. A method as set out in claim 1, wherein said slot has a single direction of lay. 
     
     
       8. A method as set out in claim 1, wherein said slot has a periodically reversing direction of lay. 
     
     
       9. A light waveguide cable, comprising: a cylindrical rod having a longitudinal axis and provided with at least one peripheral helical slot in its exterior lateral surface; and,   a radially superimposed stack comprising at least first and second relatively flat optical waveguide ribbons within said slot, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces, said first ribbon in said stack being located at a radially inward position and said second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said rod, said first ribbon being under a first tension and said second ribbon being under a second tension, said second tension exceeding said first tension when said cable is under a predetermined tensile load.   
     
     
       10. A light waveguide cable as set out in claim 9, wherein each of said light waveguides has an attenuation of less than 0.3 dB/km measured at 1550 nm at 23° C. 
     
     
       11. A light waveguide cable as set out in claim 9, wherein each of said slots proceeds along the periphery of the rod with a single direction of lay. 
     
     
       12. A light waveguide cable as set out in claim 9, wherein each of said slots proceeds along the periphery of the rod with a periodically reversing direction of lay. 
     
     
       13. A light waveguide cable, comprising: a cylindrical rod having a longitudinal axis and provided with at least one peripheral helical slot in its exterior lateral surface; and,   a radially superimposed stack comprising at least first and second relatively flat optical waveguide ribbons within said slot, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces, said first ribbon in said stack being located at a radially inward position and said second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said rod, said first ribbon being under a first tension and said second ribbon being under a second tension, said second tension exceeding said first tension when said cable is at at least a predetermined temperature.   
     
     
       14. A light waveguide cable as set out in claim 13, wherein each of said light waveguides has an attenuation of less than 0.3 dB/km measured at 1550 nm at 23° C. 
     
     
       15. A light waveguide cable as set out in claim 13, wherein each of said slots proceeds along the periphery of the rod with a single direction of lay. 
     
     
       16. A light waveguide cable as set out in claim 13, wherein each of said slots proceeds along the periphery of the rod with a periodically reversing direction of lay. 
     
     
       17. A method for making a slotted core cable for light waveguide ribbons, comprising: forming a cylindrical rod having a longitudinal axis and provided with at least one peripheral helical slot in its exterior surface;   providing at least first and second relatively flat optical waveguide ribbons, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces; and,   applying a first tension to said first ribbon and applying a second tension to said second ribbon while inserting said ribbons in said slot to form a radially superimposed stack, said first ribbon in said stack being located at a radially inward position and a second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said rod, and said second tension exceeding said first tension.   
     
     
       18. A light waveguide ribbon cable, comprising: a central element having a longitudinal axis;   a carrier disposed about said central element, said carrier including a helical slot which is open radially outward with respect to said central element axis; and,   a radially superimposed stack comprising at least first and second relatively flat optical waveguide ribbons within said slot, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces, said first ribbon in said stack being located at a radially inward position and said second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said central element, said first ribbon being under a first tension and said second ribbon being under a second tension, said second tension exceeding said first tension when said cable is under a predetermined tensile load.   
     
     
       19. A light waveguide ribbon cable, comprising: a central element having a longitudinal axis;   a carrier disposed about said central element, said carrier including a helical slot which is open radially outward with respect to said central element axis; and,   a radially superimposed stack comprising at least first and second relatively flat optical waveguide ribbons within said slot, each of said optical waveguide ribbons having two major surfaces and a thickness between said major surfaces, said first ribbon in said stack being located at a radially inward position and said second ribbon in said stack being located at a radially outward position with respect to said longitudinal axis of said central element, said first ribbon being under a first tension and said second ribbon being under a second tension, said second tension exceeding said first tension when said cable is at at least a predetermined temperature.